In a fuel cell system including a fuel cell, the fuel cell generates electric power through electrochemical reaction with supply of a fuel gas (e.g., hydrogen) and an oxidizing gas (e.g., the air). At the stopping process of the fuel cell system, the supply of the fuel gas and the oxidizing gas is stopped. After the system stop, the air may be introduced from outside of the fuel cell to the cathode, and part of the introduced air may permeate through the electrolyte membrane to reach the anode. This may raise the cathode electrode potential and cause oxidation of the carbon component material of the cathode (for example, carbon for the gas diffusion layer or carbon used as the catalyst support).
One proposed technique against this problem supplies hydrogen and fills the supplied hydrogen to the cathode during system stopping process of the fuel cell system (for example, Patent Literature 1).